Buzzing on line - UK Vintage Radio Repair and Restoration Discussion Forum

aristellier · 27th Feb 2009, 6:29 pm

Thanks to everyone who helped me sort out my last problem.
So here is my next one, I have an old gpo 746 phone which is fantastic but does have a slight buzzing on the line. When I got it I was on Virgin Media and it was crystal clear and load but as soon as I changed to Sky using a Bt line it has developed this slight buzzing and has gone a lot quieter in the earpiece. I was told to reset the Sky+ box as this can sometimescause interferance but alas no joy.
What are your thoughts
Thanks
Aris

russell_w_b · 27th Feb 2009, 8:07 pm

My thoughts are to disconnect every extension and plug your telephone into the master-box, ie: the main telephone socket where the line comes into your premises. Have you got a master-box where the lower part of the fascia can be removed (identifiable by the socket being nearer the bottom than the top of the box)? If so, removal of the two front screws and the plate it holds on will reveal a further socket to which no extension should be connected. Plug your instrument in here and listen for buzzing.

Buzzing on this, the master socket and demarcator between your telephone provider and your 'own' installation - irrespective of who installed it - will reveal a 'noisy' line (possibly an 'earthy' leg) to which BT will need to repair, free of charge. No buzzing will indicate a fault on your own wiring or equipment, and can be eliminated by removing all your telephonic equipment, bit-by-bit, and plugging it in whilst monitoring on your telephone.

Have a go at this, then report back with your findings!

dagskarlsen · 27th Feb 2009, 8:34 pm

This has to be a quess.
1) The box have a lot of other things connected, and an error in the grounding system, even outside your house may generate a hum in the telephone. (try to reverse tip/ring (a/b))
2) The powersupply it selves generates hum to the telephone part.

Try another phone if its humming too.
Measure the current when offhook, 20-25 milliAmps should be ideal.
If it is to high redusing this could fix it. Redusing the current could be done by buying a unit, or making a gadget you selves. A capacitor of 2-3 microfarad in series with the telephone, as near as possible, or inside telephone will let the speach and ringing come thru. A 1W resistor in parallel with the cap wil let thru the dc. Try different values until you get a good result.
I belive the 746 was designed for long lines, so will sugest to start with a resistor of 300 ohms or more.

If you cant put the current adjuster in the phone, you may have to make 2 one one each line. The caps are not critical, but the resistors should be equal and have a total of ohms equal to the one you would put into the phone.

Place the phone at least 1m (yd) away from the TV.

Tell us how it went.

dsk

AndiiT · 27th Feb 2009, 9:03 pm

Hi,
You mention that you now have Sky, presumably the Sky Digital set top box is connected to the phone line - I have had numerous occasions where disconnecting the phone line feed (at the line jack end) to the Sky set top box has removed the buzz from the line; this is often due to pick up of the televisions timebase on the line cord.

Sky require that you leave the phone line connected to the Set top box though so if you do prove that what is mentioned above that is causing the buzz you could try relocating the line cord away from the source of interference or perhaps wrapping a few turns of line cord around a ferrite ring or two.

Hope this helps.

Andrew

paulsherwin · 27th Feb 2009, 9:18 pm

New ADSL connections do tend to suffer from line noise on the POTS phones until everything settles down. Better microfilters may help, and some phones don't play well with ADSL (not necessarily the phone you're using at the time).

As others have said, disconnect *everything* except a single phone and see if the noise is still there. Assuming it isn't reconnect the router via a microfilter and see if the noise has started. If there's still no noise, reconnect everything one device at a time until the noise starts.

I found a lot of noise was being added to my phone circuit by a phone/clock radio unit in the bedroom. This was fine before ADSL was installed.

Paul

aristellier · 27th Feb 2009, 10:47 pm

Thanks, that gives me alot to be going on with. I'll give it go on my next day off and report back.

27th Feb 2009, 6:29 pm	#1
aristellier Retired Dormant Member Join Date: Feb 2009 Location: Poole, Dorset, UK. Posts: 6	Buzzing on line Thanks to everyone who helped me sort out my last problem. So here is my next one, I have an old gpo 746 phone which is fantastic but does have a slight buzzing on the line. When I got it I was on Virgin Media and it was crystal clear and load but as soon as I changed to Sky using a Bt line it has developed this slight buzzing and has gone a lot quieter in the earpiece. I was told to reset the Sky+ box as this can sometimescause interferance but alas no joy. What are your thoughts Thanks Aris

27th Feb 2009, 8:07 pm	#2
russell_w_b Dekatron Join Date: Jul 2007 Location: Penrith, Cumbria, UK. Posts: 3,687	Re: Buzzing on line My thoughts are to disconnect every extension and plug your telephone into the master-box, ie: the main telephone socket where the line comes into your premises. Have you got a master-box where the lower part of the fascia can be removed (identifiable by the socket being nearer the bottom than the top of the box)? If so, removal of the two front screws and the plate it holds on will reveal a further socket to which no extension should be connected. Plug your instrument in here and listen for buzzing. Buzzing on this, the master socket and demarcator between your telephone provider and your 'own' installation - irrespective of who installed it - will reveal a 'noisy' line (possibly an 'earthy' leg) to which BT will need to repair, free of charge. No buzzing will indicate a fault on your own wiring or equipment, and can be eliminated by removing all your telephonic equipment, bit-by-bit, and plugging it in whilst monitoring on your telephone. Have a go at this, then report back with your findings! __________________ Regds, Russell W. B. G4YLI.

27th Feb 2009, 8:34 pm	#3
dagskarlsen Heptode Join Date: Jan 2008 Location: Hakadal, Norway Posts: 643	Re: Buzzing on line This has to be a quess. 1) The box have a lot of other things connected, and an error in the grounding system, even outside your house may generate a hum in the telephone. (try to reverse tip/ring (a/b)) 2) The powersupply it selves generates hum to the telephone part. Try another phone if its humming too. Measure the current when offhook, 20-25 milliAmps should be ideal. If it is to high redusing this could fix it. Redusing the current could be done by buying a unit, or making a gadget you selves. A capacitor of 2-3 microfarad in series with the telephone, as near as possible, or inside telephone will let the speach and ringing come thru. A 1W resistor in parallel with the cap wil let thru the dc. Try different values until you get a good result. I belive the 746 was designed for long lines, so will sugest to start with a resistor of 300 ohms or more. If you cant put the current adjuster in the phone, you may have to make 2 one one each line. The caps are not critical, but the resistors should be equal and have a total of ohms equal to the one you would put into the phone. Place the phone at least 1m (yd) away from the TV. Tell us how it went. dsk

27th Feb 2009, 9:03 pm	#4
AndiiT Octode Join Date: Aug 2005 Location: Saltburn-East, Cleveland, UK. Posts: 1,786	Re: Buzzing on line Hi, You mention that you now have Sky, presumably the Sky Digital set top box is connected to the phone line - I have had numerous occasions where disconnecting the phone line feed (at the line jack end) to the Sky set top box has removed the buzz from the line; this is often due to pick up of the televisions timebase on the line cord. Sky require that you leave the phone line connected to the Set top box though so if you do prove that what is mentioned above that is causing the buzz you could try relocating the line cord away from the source of interference or perhaps wrapping a few turns of line cord around a ferrite ring or two. Hope this helps. Andrew

27th Feb 2009, 9:18 pm	#5
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,970	Re: Buzzing on line New ADSL connections do tend to suffer from line noise on the POTS phones until everything settles down. Better microfilters may help, and some phones don't play well with ADSL (not necessarily the phone you're using at the time). As others have said, disconnect everything except a single phone and see if the noise is still there. Assuming it isn't reconnect the router via a microfilter and see if the noise has started. If there's still no noise, reconnect everything one device at a time until the noise starts. I found a lot of noise was being added to my phone circuit by a phone/clock radio unit in the bedroom. This was fine before ADSL was installed. Paul

27th Feb 2009, 10:47 pm	#6
aristellier Retired Dormant Member Join Date: Feb 2009 Location: Poole, Dorset, UK. Posts: 6	Re: Buzzing on line Thanks, that gives me alot to be going on with. I'll give it go on my next day off and report back.